Semiconductor fabrication faces shrinking device dimensions and increasing process complexity. Devices of today are smaller and require more fabrication processes than devices of even a few years ago. Additionally, the shrinking dimensions require ever tighter tolerances for performance of the process employed in semiconductor fabrication. Semiconductor manufacturers generally recoup their manufacturing costs by selling their fabricated semiconductor devices. However, some semiconductor devices fail to meet operational requirements and are, therefore, unable to be sold. As a result, the manufacture does not recoup the manufacturing costs for the failed devices.
A critical statistic in semiconductor fabrication is yield, which is a percentage of devices fabricated that meet operational requirements. A goal of device fabrication process is to reach 100 percent yield, although this goal is not generally obtained. However, the closer to this goal and the higher the yield, the greater the profitability for manufacturer.
Semiconductor fabrication processes and the devices themselves are very sensitive to out of tolerance process conditions, mishandling, movement, temperature, humidity, and the like. As a result, defects in structures and layers present in semiconductor devices can occur. For example, inappropriate transferring of a boat containing wafers can result in defects formed on a number of devices located on those wafers.
Typical semiconductor devices can have relatively large numbers of defects present, such as 1,000 defects. However, fortunately, a large number of defects are not harmful, for example 880 out of the 1,000 defects. For example, hillock formations can occur in conductive layers within metallization layers and not substantially degrade device performance. But, other defects, such as unfilled trenches, are harmful, for example 20 out of the 1,000 defects, do degrade performance. Therefore, it is noted that classifying and identifying defects as harmful is important. Harmful defects can be analyzed and causing conditions identified. Corrections can then be made, such as altering process parameters and/or design layout, that mitigate occurrence of such defects in the future. However, properly classifying defects into harmful and harmless categories requires substantial time and expertise by trained personnel. This reduces the ability of semiconductor device manufactures to identify harmful defects and take proper corrective action to mitigate or prevent harmful defects from occurring in the future. As a result, yield values are unfortunately lowered.